1. Field of the Invention
The present invention relates to a parallax barrier for use in combination with a display panel and for permitting each different image to be displayed to different display directions of the display panel. The present invention also relates to a multiple display device including the combination of the display panel and the parallax barrier, the multiple display device being capable of displaying each different image to different display directions. The present invention also relates to a method of manufacturing the parallax barrier.
2. Description of the Related Art
There have been proposed display devices that can display each different image to different directions of one display screen (multiple display). Such multiple display devices are proposed as devices having a display panel in combination with a parallax barrier. Technologies of such multiple display devices are disclosed in documents, such as Japanese Unexamined Patent Publication No. 2004-206089 (published on Jul. 22, 2004), Japanese Unexamined Patent Publication No. 2005-78076 (published on Mar. 24, 2005), Japanese Unexamined Patent Publication No. 2005-78080 (published on Mar. 24, 2005), and Japanese Unexamined Patent Publication No. 2005-78094 (published on Mar. 24, 2005).
As illustrated in FIG. 7, in the multiple display device (in FIG. 7, a dual display device is illustrated as an example), a first image and a second image, which are displayed on a display panel 110, are given specific viewing angles by a parallax barrier 120 provided outside the display panel 110. Thereby, as illustrated in FIG. 8, the different images can be displayed to different observers in different observation positions.
The parallax barrier usually includes a light-blocking layer that is formed by patterning a metal layer or a resin layer on a glass substrate or the like. The patterning of the light-blocking layer is carried out by photolithography.
In such a multiple display device including the display panel and the parallax barrier in combination, as illustrated in FIG. 9, a barrier pitch distance of the parallax barrier and a pixel pitch distance of the display panel are almost equal. What is meant by the term “pixel pitch distance of the display panel” herein is a pitch distance between adjacent pixels on the display panel. The term “pixel pitch distance” herein is defined as a pixel pitch distance between the pixels whose viewing angles are controlled in the same direction. In other words, the term “pixel pitch distance” herein is a pixel pitch distance between the pixels on a display image that is displayed to the left, or on a display image that is displayed to the right.
However, in fact, visibility obtained by an arrangement in which the pixel pitch distance and the barrier pitch distance are set so as to be slightly different, is better than visibility obtained by the arrangement in which the pixel pitch distance and the barrier pitch distance are equal. This is described below with reference to FIGS. 10A and 10B.
FIG. 10A illustrates a case wherein a pixel pitch distance and a barrier pitch distance are exactly equal. In this case, viewing angles, which are controlled by a parallax barrier, are uniform over the entire screen, and rays of display light that give the best visibility (solid arrows in FIG. 10A) are parallel to each other over the entire screen.
However, rays of display light that are actually observed by an observer (dashed arrows in FIG. 10A) are not parallel to each other over the entire screen. For example, if the rays of display light from the center of the screen can be observed by the observer with the best visibility, the rays of display light from a peripheral area of the screen cannot be observed by the observer with the best visibility. Therefore, the entire screen visibility for the observer is not uniform.
That is, in order to attain uniform visibility for the observer over the entire screen, it is preferable to provide an arrangement such as that illustrated in FIG. 10B, viewing angles are controlled to be different per each display position by the parallax barrier, so that the rays of display light that can be observed with the best visibility (solid arrows in FIG. 10B) converge to an assumed observation position.
The viewing angle properties illustrated in FIG. 10B can be obtained with the arrangement in which the barrier pitch distance of the parallax barrier and the pixel pitch distance of the display panel are slightly different. More specifically, in the case where a parallax barrier is placed in front of a display panel, the barrier pitch distance is set to be shorter than the pixel pitch distance. Moreover, in the case where parallax barrier is placed behind a display panel (this is possible in the case where the display panel is a transmissive liquid crystal display panel), the barrier pitch distance is set to be longer than the pixel pitch distance.
However, the conventional arrangements described above have the following difficulty in manufacturing the parallax barrier.
That is, in the case where the barrier pitch distance of the parallax barrier and the pixel pitch distance of a display panel are slightly different, the difference in pitch distance between the pixel pitch distance and the barrier pitch distance is extremely small. Therefore, for achieving a desired barrier pitch distance of the parallax barrier, a mask used for achieving the desired barrier pitch distance must be manufactured with extremely high accuracy. Therefore, it is difficult to obtain the mask having the necessary extremely high accuracy using a current mask drawing technology for liquid crystals.